In order to realize a thin and simple-structured planar illuminating device which is capable of carrying out the regional light control, a backlight module 1 of the present invention includes a light guiding plate 2 including steps 21a, 21b, and 21c, a plurality of LEDs 3 provided in the vicinity of one side surface of the light guiding plate 2, and light guides 4a, 4b, and 4c which are provided respectively between each of the steps 21a, 21b, 21c and each of the LEDs 3 facing each other. The regional light control is possible by controlling brightness of each of the LEDs 3. Each of the regions is formed so as to correspond to each of the bottom surfaces 22a, 22b, 22c, and 22d.